Vortical structures around a surface-mounted pyramid in a thin boundary layer

The results of an experimental investigation of the flow around surface-mounted, sharp-edged pyramids in thin boundary layer flows are presented. Oil-film flow visualizations, PIV and LDV are used to document the flow field. For slender pyramids (ζ<75°), periodic flow in the wake of the slender pyramid is a result of regular vortex shedding. Two pairs of counter-rotating vortices exist on the side faces. One of these extends to the wake and sheds alternately from opposite sides. The other pair forms the rotor vortex downstream of the pyramid apex. A pair of counter-rotating vortices in the near wake are vertically extended and tilted downstream. The flow pattern is similar to an owl-face of the second kind.